Innovations in device architectures and materials promote transistor miniaturization for improved performance, energy efficiency and integration density. At foreseeable ångström nodes, a gate-all-around (GAA) field-effect transistor based on two-dimensional (2D) semiconductors would provide excellent electrostatic gate controllability to achieve ultimate power scaling and performance delivering. However, a major roadblock lies in the scalable integration of 2D GAA heterostructures with atomically smooth and conformal interfaces. Here we report a wafer-scale multi-layer-stacked single-crystalline 2D GAA configuration achieved with low-temperature monolithic three-dimensional integration, in which high-mobility 2D semiconductor Bi